This invention relates to a process for molding a hydrophilic contact lens in a two part mold that simultaneously forms both the front and rear surfaces of the lens. The lens is produced by placing hydrophilic lens forming monomer in a first mold part, forming a contact lens shaped cavity by mating the first mold part with a second mold part, and polymerizing the monomer to form a contact lens in the cavity.
When molding a hydrophilic lens, lens forming monomer may be mixed with a solvent. This achieves several advantages. Use of solvent helps to produce lenses having reproducible size and shape. The use of solvent in the monomer mixture minimizes the shrinkage of the monomer mixture during polymerization, thereby improving lens quality. The solvent distributes heat more evenly during polymerization.
Polymerization solvents used in the past are typically organic liquids having relatively high boiling points, such as ethylene glycol (Refojo Journal of Polymer Science: Part A-1, Vol. 5,3103-3113 (1967)), compounds falling within a specific viscosity and R-Value range (Larsen, et al., U.S. Pat. No. 4,680,336) and boric acid esters of ethylene glycol (Kindt-Larsen, et al., U.S. Pat. No. 4,889,664). Other publications disclosing use of solvents for molding include U.S. Pat. Nos. 3,532,679; 3,660,545; and 3,948,841.
In the past removal of solvent from the molded polymer has been done by liquid-liquid extraction to replace the solvent with saline. This can be a tedious, expensive and time-consuming process